Variable condenser



March 7, 1939. E. s. MARIS I 2,149,702

' VARIABLE CONDENSER File'd June so, 1956 3nventor Patented Mar. 7, 1939UNITED STATES VARIABLE CONDENSER Elwood S. Maris, Upper Darby, Pa.,assignor to Radio Corporation of Delaware Application June 30,

3 Claims.

This invention relates to electrical condensers and particularly tovariable air-condensers of the so-called trimmer type.

An object of the invention is to provide a capacitor, the operation ofwhich is characterized (a) by a high degree of stability under extremeconditions of climate, (b) by ease of adjustment and (0) by absence ofmicrophonic and other.

parasitic disturbances.

Another object of the invention is to provide a simple, inexpensive,compact, trouble-free capacitor and one which lends itself readily tomass production methods.

A more specific object of the invention is to provide a variablecondenser having a fixed armature, a slldable armature and a guidewayfor the latter molded in, rigid permanent alignment with the fixedarmature.

Other objects and advantages of the invention together with certaindetails of construction and assembly will be apparent and the inventionitself will'be best understood by reference to the following descriptionand to the accompanying drawing, wherein Figure 1 is a longitudinalsectional view of an air-type variable condenser constructed inaccordance with the principle of the invention, Fig. 2 is an enlargedcross-sectional view taken on the line 2-2 of Fig. 1,

Fig. 3 is a longitudinal sectional view of certain of the parts of thecondenser of Fig. I mounted on a mandrel and illustrating the manner ofaligning these elements during assembly, and

Fig. 4 is alongitudinal sectional view of the condenser parts andmandrel of Fig. 3 inserted within a mold within which metal lugs arecast for maintaining the elements constituting the flxed parts of thecapacitor in permanent alignment. r 1

Referring now to the drawing in which like reference charactersrepresent the same or correspondingparts. The bodyofthevariablecondenser of Fig. 1 is constituted by a pair of conductivetubes' In and 20 arrangedin spaced end-to-end 5 relation and a hollowinsulating member 30 spanning the space therebetween. Conductive tubesin and 20 each has a metal cup shape member designated at H and 2|,respectively, intimately joined thereto and in which the Opposite endsof the hollow insulating member 30 are immovably seated.

Conductive tube Ill constitutes one armature or electrode of thecondenserpthe diameter of its bore is greater than that of conductivetube 20. Armature tube I0 is provided with'an' outwardly America, acorporation of 1936, Serial No. 88,125

extending peripheral rim l2. A wire lead to looped about tube I0 isclamped between the outer wall of this rim [2 and the adjacentcircumferential edge of the insulating tube 30. The

other conductive tube 20 is provided with a pair of rims 22 and 22a, theinner side wall of the first rim 22 contacts the oppositecircumferential edge of insulating tube 30. Rims l2 and 22 preferablyhave non-circular peripheries (see Fig. 2), or they may be knurled toprevent movement with respect to the cup shape members H and 2l in whichthey are embedded. The other or second armature comprises a conductiverod 40 having a diameter corresponding substantially to that of the boreof the smaller conductive tube 20. Armature 40' slidably contacts theinner wall of conductive tube 20, which tube is of sufficient length toconstitute a support capable of maintaining that part of rod 40 whichextends therebeyond against undesired lateral movement with respect tothe inner wall of the tube-like armature- III. The diameter of therod-like armature III is less than that of the bore of the armature Illwhereby an air gap is established therebetween. The terminal end of thatportion of rod III which is presented to the interior of tube Illcarries an insulating annulus ll of a diameter sufficient to close theair space s between these two armatures against moisture and dust.Annulus 4| further prevents displacement of armature 40 with respect tothe inner walls of armature In. The end portion 42 of the rod-likearmature 40 adjacent the annulus 4| is preferably beveled, as shown in.Fig. 1 to provide a receptacle for such dust and minute metal particlesas may result from abrasive contact between 4| and the inner wall oftube Ill. The opposite terminal end of rod I0 is provided with akey-hole 43 adapted to receive a key (not shown) which may be used tofacilitate movement of rod ll, whereby to achieve a desired capacitanceby altering the effective armature area presented by (0 to the innerwalls of conductive tube Hi.

That portion of the outer wall of the conductive supporting tube 20which extends beyond insulating tube 3! and its supporting cup 2| isprovided with a D-shape screw-threaded portion 23 and a bifurcatedcylindrical end section 24 which terminates in a beveled edge 25. Thescrewthreaded portion 23 receives a nut 26 for clamping the device to apanel or base p of the radio apparatus (not shown) to which thecondenser lead 10 extends. Screw threads 23 also receive a second nut 21which has a beveled collet or shoulder portion 28 which engages thebeveled edge 25 of the bifurcated portion 24 of the conductive armaturesupporting tube 20, and compresses it tightly against the siidablerod-like armature, whereby to clamp it securely against movement in adesired relative position.

One very important feature of the condenser 01 the invention is that theparts iii, 2d and 3d constituting'its main body portion are Joined oneto another in permanent fixed alignment by molding first fitted on themandrel and thepre-formed looped end of conductive lead w placed aboutthe outer surface of tube iil'in contact with-its peripheral rim 12. Thehollow insulating shell is then slid into position with its inner endoverlapping a portion of the armature tube l0 and its inner edge againstthe wire lead 10. Conductive tube 20 is then placed over the reduceddiameter portion 52 of the mandrel 50 with its inner end fitted withinthe insulating shell 30 and its inner rim 22 in contact with the edge ofthis shell 30.

With the armature l0, lead wire w, insulating shell 30 and conductivetube 20 positioned in the described manner on mandrel 50 the assembly isinserted in a moldBll (Fig. 4) with the lead wire to projecting througha hole 5|, provided for the purpose, in its lower section 62. The uppersection v.63 of the mold is provided" with two holes 64 and'65 to permitthe introduction of the molten metal which eventually forms thecup-shape members H. and 2| (Fig. 1) which surround the terminal edgesof the insulating shell 3|]. Preferably the shell 30 is provided withsemi-peripheral grooves 3|, 3la adjacent its ends and into which themetal flows. These grooves 3i, like the non-circular peripheral contourof metal rims i2 and 22 prevent the possibility of relative axialmovement of the parts after themetal cups Ii and 2| have been'cast. Y

When the casting operation has been completed and the assembly removedfrom the mold, the mandrel 50 is withdrawn and .the rod-like armature 40slidably inserted into the conductive supporting tube 20 so that aportion of its surface extends within, but out of contact with, thetube-like armature Ii].

It is to be understood that the foregoing description of a preferredembodiment of the invention is to be interpreted as'illustrative and notin a limiting sense except as required by the prior art and the spiritof the appended claims.

' What is claimed is':

l. {i variable condenser comprising a pair of hollow conductive tubesarranged in spaced ,coaxial relation, a hollow insulating memberspanning the space therebetween, means including said insulating memberfor maintaining said tubes in rigid insulated alignment, said tubeshaving bores of difierent diameter, a terminal end of the tube ofsmaller bore being bifurcated to render it resilient and the tube oflarger bore constituting an armature of said condenser, a secondarmature for said condenser comprising a conductive rod extending intoboth said tubesfor.

relation, one of said tubes constituting an arma-.

ture of said condenser, a hollow insulating member spanning the spacebetween said tubes, 2. pair of said insulating member are immovablyseated, and a rod-like armature extending through one of said tubes inslidable contact with the inner wall thereof and into, but out ofcontact with the walls of, said armature tube.

3. A variable condenser in accordance with claim 1 and wherein aterminal connection for said armature tube extends outwardly therefromthrough the body of one of the cup-shape members in which said hollowinsulating member is seated.

ELWOOD S. MARIS.

- of cup-shape members intimately joined respectively to said tubes andin which the opposite ends

